1. Field of the Invention
The present invention relates to a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device which is capable of reducing occurrence of nonuniform display caused by warp in a liquid crystal display portion due to an external environment.
2. Description of the Related Art
A liquid crystal display device has advantages of high display performance, low power consumption, a low profile, being lightweight, and the like, and is now widely applied to, for example, a cellular mobile phone, a digital camera, a monitor for a personal computer (PC), and a television (TV) set.
FIGS. 1 and 2 illustrate structures of a typical liquid crystal display device. In FIG. 1, a liquid crystal display portion 6 includes a first polarizing plate 1 on a light incident side and a second polarizing plate 2 on a light emitting side. A liquid crystal layer 5 is provided between a first substrate 3 and a second substrate 4. An electrode group is provided on at least one of the first substrate 3 and the second substrate 4 so that voltage is applicable to the liquid crystal layer 5 with respect to each pixel. A backlight device 10 includes a light source 7, a backlight device frame 8, and an optical member group 9.
In a typical liquid crystal display device, the substrates 3 and 4 are made of glass and their expansion coefficient which depends on an external environment (temperature and humidity) greatly differs from that of the polarizing plates 1 and 2. As a result, as described in JP 2003-279748 A, the liquid crystal display portion 6 warps depending on a state of the backlight device (power on/off and applied power) and an external environment (weather and geographic area).
Referring to FIG. 2, in the typical liquid crystal display device, the liquid crystal display portion 6 is mounted on the backlight device 10 and is fixed by a frame member 8-1. Therefore, when the liquid crystal display portion 6 warps to a great extent, the liquid crystal display portion 6 is brought into contact with the frame member 8-1 or the optical member group 9. Here, part of the liquid crystal display portion 6 is pressed from the front or from the rear, which disturbs orientation of liquid crystal molecules in the liquid crystal layer 5, resulting in occurrence of nonuniform display.
JP 2005-301147 A discloses a method of joining a backlight device and a liquid crystal display portion together for the purpose of preventing distortion of sheet-like optical members of the backlight device. This method enables prevention of distortion and misalignment of the optical members. However, according to study by the inventors of the present invention, the extent of the above-mentioned warp in the liquid crystal display portion becomes greater on the contrary.
Conventionally, when warp in a liquid crystal display portion becomes a problem, as illustrated in FIG. 2, the frame member 8-1 and a frame member 8-2 are provided so that there is a sufficient clearance between the liquid crystal display portion 6 and the frame member 8-1 or between the liquid crystal display portion 6 and the optical member group 9. However, if those clearances are too large, such a problem of mechanical reliability arises that the liquid crystal display portion 6 is not fixed and misalignment occurs.
Further, JP 2008-243803 A describes a liquid crystal display device in which an optical member group and a liquid crystal display portion are joined together; JP 2007-65644 A, a resin substrate material and a glass material whose amounts of strain are small; JP 2005-302336 A, a low refractive index layer; and JP 3448626 B, a reflective polarizer which functions as required by a structure in an optical member.
The above-mentioned problem which accompanies warp in a liquid crystal display portion is expected to become more obvious in the future in accordance with the recent trend toward a greater display of a liquid crystal display device and higher quality of display of a liquid crystal display device.